1. Technical Field
The present invention relates to methods and apparatus for supplying power and is especially useful for supplying power to a highly dynamic load.
2. Background Art
Power supplies and amplifiers are well known in the art. A variety of configurations and topologies have been developed over the years to provide electrical power to a load. Loads that have widely varying impedances, however, provide a challenge to traditional power supplies driven by conventional techniques. One particular challenge involves finding a power supply or amplifier capable of supplying a variety of waveforms to drive a dynamic, widely varying load such as a flash lamp.
Flash lamps are of particular interest because of the difficulty of driving a flash lamp is the very dynamic nature of the load. When a flash lamp varies impedance to a point where the impedance is lower than the output impedance of the flash lamp, more energy is dissipated in the amplifier than in the load. This may end up (in other topologies) heating up of switches and the energy is dissipated as heat. For example, as current is sourced through the lamp, the impedance of the lamp changes in a negative way. With a fixed impedance load, as current is increased, the voltage drop across the fixed load proportionally increases also. With a flash lamp, this does not occur because the lamp becomes more conductive as more current is sourced into it. The voltage drop stays the same or it may go down (this is known as negative impedance). For most amplifiers, this has an appearance of a dead short occurring on the output. It appears as a varying load that is approaching a dead short at a very critical time. These qualities of a flash lamp make them particularly difficult to drive. Additionally, some known power supplies heat the flash lamps too quickly which may result in premature failure of the lamps.
Power supplies and amplifiers that can provide pulse width modulation output (PWM) are of particular interest. Some known configurations or topologies that can provide a PWM output to control power include push pull, bridge inverter, and flyback topologies. Known amplifiers with these topologies may provide rectangular pulses delivered to a transformer at a regular period. However, these known power supplies use rectangular pulses delivered to a transformer at a regular period and throttle the duty cycle forwards or backwards (greater or less) depending on the current need of the load. Most switching power supplies that are in many common place items are driven to operate in this manner.
Traditional resonant power supplies cannot provide variable energy per pulse. Rather the energy per pulse is fixed requiring fewer pulses per unit time be delivered to reduce output energy and more pulses per unit time to increase energy. This method in effect removes pulses which will cause the flash lamp to extinguish at low energy levels. Traditional PWM controlled power supplies use switch on time duty cycle to control energy and thus offer limited control range.
Accordingly, there is an un-met need to provide power supplies and amplifiers that can be configured to generate variable waveforms and used to power a highly dynamic load such as a flash lamp.